Is the idea that watermelons have male and female sexes a folk saying, and will the seeds of a "male" watermelon still sprout?
Watermelons are not divided into male and female. If variety degeneration is not taken into account, the watermelon seeds produced can all be used as seeds!
The question of male and female watermelons is probably also a folk saying: a watermelon with a large "navel" is said to be female, while one with a small one is said to be male. In fact, this saying has no basis at all. Watermelon is a plant with separate male and female flowers on the same plant, so no matter what kind of watermelon it is, it develops from a female flower after fertilization. In other words, no matter what kind of watermelon it is, as long as it produces female flowers, it may be fertilized and set fruit.
Whether a watermelon seed can sprout and be used as seed depends to a large extent on how well the seed has developed. Many watermelon seeds have not developed enough to maturity and may even have difficulty sprouting. But even for watermelon seeds that can sprout, it is still not recommended to use them as seeds.
If you pay attention, you will find that the watermelon seeds on the market today are basically all hybrids! For hybrids, once seeds are saved, variety degeneration will occur. I have also explained this issue many times. If you understand seed production techniques, then you can save seeds, propagating the parents generation after generation, purifying them, and producing hybrids, but if you do not understand these things, it is still not recommended to save seeds.
In addition, there is the matter of seedless watermelons. Although they are called seedless watermelons, you can still see immature seeds, and although there are few, there are still some. Such seeds definitely do not have the ability to be used as seeds, and do not even have the ability to sprout. (Seedless watermelons are propagated from seeds produced by crossing diploid watermelons with tetraploid watermelons.)